The TheRAPy vanguard trial is a multicentre, multiple period randomized, cluster crossover vanguard trial testing the feasibility of a full-scale trial to evaluate whether a centre-based policy of routine use of RAP versus a policy of crystalloid priming reduces RBC transfusion for patients undergoing cardiac surgery on cardiopulmonary bypass. It will also provide information about key parameters of the TheRAPy full-scale trial.

About 50% of patients undergoing cardiac surgery require red blood cell (RBC) transfusion. Given the limited blood supply and harms of transfusion, evidence-based blood conservation strategies are a priority. There is one such simple conservation technique called Retrograde autologous priming (RAP), in which the patient's own blood, rather than crystalloid fluid, is used to prime the heart-lung machine. Ultimately, it minimizes the loss of RBCs during surgery. Despite evidence of RAP reducing incidence of RBC transfusions by 40% and RBC units transfused by 38% in small randomized trials, it is not routinely used due to the uncertainty about overall benefit and potential harms. Routine RAP may be beneficial, but this needs to be confirmed in a large pragmatic randomized trial. Therefore, the goal of this vanguard trial is to assess the feasibility of a full-scale multi-centre randomized cluster crossover trial to determine whether an institutional policy of routine RAP reduces the number of RBC units transfused up to 72 hours after cardiac surgery compared to crystalloid priming. This will include 4 sites that will test the two policies in an alternating sequence during 12 periods of 4 weeks, with an expected volume of 4500 cardiac surgery patients. If the adherence to both polices is >=90%, a full trial will be conducted. The findings of this study have the potential to improve the outcomes of tens of thousands of patients around the world and will provide the basis for cardiac practice guidelines.

Inclusion Criteria:

• Hospitals completing >200 adult cardiac surgical cases a year; (ii) 95% of cardiovascular surgery group (i.e., cardiac anesthesiologists, surgeons, and perfusionists) agree to manage patients under both autologous priming policies as per their randomization schedule for the duration of the trial.
• All patients undergoing cardiac surgery on cardiopulmonary bypass at an enrolled site during the trial period will be included in data collection.

Exclusion Criteria:

• Complete <=200 cardiac surgical cases.
• <95% of their cardiovascular surgery group agrees to manage patients according to either of the two policies.